Assuming that Asus actually called it “Line-In/Headphone,” then you need to switch to Line-In in Windows sound management before Audacity will get the audio. It’s pretty common for a computer not to have the right drivers and support software for Windows 10. Check with Asus for updates.
If nothing works, you may need something like a Behringer UCA-202 to go between the computer and your cassette deck. Here’s one between my stereo sound mixer and my Windows machine.
Other people make adapters like this.
https://forum.audacityteam.org/t/sound-card-reviews/8375/1
People also make adapters that just duplicate what you already have. Don’t buy those.
Koz